U.S. patent number 4,873,154 [Application Number 07/151,722] was granted by the patent office on 1989-10-10 for magnetic recording medium containing fe, co, n and o.
This patent grant is currently assigned to Fuji Photo Film Co., Ltd.. Invention is credited to Akio Yanai, Tadashi Yasunaga.
United States Patent |
4,873,154 |
Yasunaga , et al. |
October 10, 1989 |
Magnetic recording medium containing Fe, Co, N and O
Abstract
A magnetic recording medium, such as a tape, having a thin
ferromagnetic film containing Fe.sub.a Co.sub.b N.sub.c O.sub.d
satisfying: 32%.ltoreq.a.ltoreq.90%; 5%.ltoreq.b.ltoreq.55%;
2%.ltoreq.c.ltoreq.28%; 5%.ltoreq.d.ltoreq.23%; and c+d.ltoreq.40%.
Such a film provides enhanced resistance against corrosion.
Inventors: |
Yasunaga; Tadashi (Kanagawa,
JP), Yanai; Akio (Kanagawa, JP) |
Assignee: |
Fuji Photo Film Co., Ltd.
(Kanagawa, JP)
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Family
ID: |
12136526 |
Appl.
No.: |
07/151,722 |
Filed: |
February 3, 1988 |
Foreign Application Priority Data
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Feb 4, 1987 [JP] |
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62-24378 |
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Current U.S.
Class: |
428/836.2;
G9B/5.24; 427/132; 428/900; 427/128; 428/702 |
Current CPC
Class: |
G11B
5/656 (20130101); Y10S 428/90 (20130101) |
Current International
Class: |
G11B
5/64 (20060101); G11B 005/64 () |
Field of
Search: |
;428/694,702,900,336
;427/128,132 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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122030 |
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Oct 1984 |
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EP |
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207426 |
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Nov 1984 |
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JP |
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Primary Examiner: Lesmes; George F.
Assistant Examiner: Monroe; J. B.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak, and
Seas
Claims
What is claimed is:
1. A magnetic recording medium, comprising a non-magnetic support
having provided thereon a thin ferromagnetic metal film comprising
iron of atomic percentage a, cobalt of atomic percentage b,
nitrogen of atomic percentage c and oxygen of atomic percentage d,
wherein said atomic percentages of said iron, cobalt, nitrogen and
oxygen are based on the total number of these atoms and have the
following limits:
2. A magnetic recording medium as recited in claim 1, wherein said
atomic percentages are further limited to:
3. A magnetic recording medium as recited in claim 1, wherein c is
approximately 10 and 10.ltoreq.d.ltoreq.17.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium having
a thin ferromagnetic metal film and more particularly it relates to
a magnetic recording medium having excellent anti-corrosive
property.
2. Background Art
The demand for higher recording density in a magnetic recording
system has recently increased. In this connection, a thin metal
film type magnetic recording medium having a thin ferromagnetic
metal film formed by a vacuum evaporation method or a sputtering
method has been studied as a replacement for a conventional coating
type magnetic recording medium for a recording layer.
In such a thin metal film type magnetic recording medium, there is
formed a thin metal film composed of ferromagnetic metal alloy
having high saturation magnetization and having a thickness of from
50 to 500 nm. Accordingly, the thickness of the magnetic layer is
decreased one or two orders of magnitude below the thickness of the
conventional coating type magnetic layer, thereby reducing the
effects of demagnetization in the short wavelength region, and thus
high density recording has been realized. Furthermore, in this thin
metal film type, it is unnecessary to use organic solvents in a
large amount unlike the coating type of magnetic film, and
therefore, the manufacturing equipment can be simplified.
The types of ferromagnetic materials include iron, cobalt, nickel
or alloys thereof. When cobalt is used, the desirable high coercive
force can be relatively easily obtained due to its high monoaxial
crystal magnetic anisotropy. For example, a cobalt nickel alloy
thin film prepared as a magnetic tape by an inclined vapor
deposition method has widely been studied.
In order to improve the environmental resistance and durability of
such a thin metal film type magnetic recording medium, a method of
nitrogenating the surface of a magnetic layer by an ion plating
method has been disclosed in Japanese Patent Application (OPI) No.
33806/1975. (The term "OPI" used herein means an unexamined
published application.) A method of providing a silicon nitride
film by sputtering has been disclosed in Japanese Patent
Application (OPI) No. 30304/1978. A method of forming a
non-magnetic layer on a magnetic layer by exposing the magnetic
layer to the discharge of nitrogen gas has been disclosed in
Japanese Patent Application (OPI) No. 85403/1978. A method of
providing a nitrogenated metal thin film on a thin magnetic metal
film has been disclosed in Japanese Patent Application (OPI) No.
143111/1979. A thin magnetic film composed of iron nitride, or iron
and iron nitride has been disclosed in European Patent No. 8328 and
Japanese Patent Application (OPI) No. 87809/1984. Further, one of
the inventors of the present invention with others suggested in
their earlier application (Japanese Patent Application (OPI) No.
54023/1986) a magnetic recording medium comprising a non-magnetic
support having provided thereon a thin magnetic film mainly
comprised of iron nitride oxide. The composition of the thin
magnetic film is shown by the following composition.
A commonly assigned U.S. patent application, Ser. No. 133,829,
filed Dec. 16, 1987 also discloses an iron nitride oxide magnetic
film in which x+y.ltoreq.0.25.
On the other hand, a cobalt chromium alloy thin film prepared for a
magnetic disk by a sputtering method has been extensively
studied.
The magnetic layer of the above medium has an apparent mirror-like
surface, but microscopically has a structure having metallic fine
particles of a particle size from 10 to 100 nm. Therefore, when dew
condenses on the magnetic layer or when the magnetic recording
medium is exposed to an atmosphere containing gaseous sulfurous
acid, the magnetic recording medium easily corrodes. Even if an
extremely slight amount of corrosion is present on the surface of a
magnetic recording medium, it comes off when the medium rubs
against a magnetic head or other parts, thereby causing head
clogging or dropouts.
In order to remove the above defect, an inorganic or organic
protective layer on a thin metal film has been proposed.
However, if the above-described protective layer is provided, it
must be thick to obtain good results, which is unfavorable in view
of spacing loss. The above-described magnetic recording medium
which is mainly comprised of iron nitride or iron nitride oxide has
improved environmental resistance and improved anti-corrosive
property, but still there is a defect in that saturation
magnetization is not high enough to obtain high outputs.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic
recording medium having good anti-corrosive property and high
magnetic properties, which is free from the above-described
defects.
BRIEF DESCRIPTION OF THE DRAWING
The single drawing shows an apparatus for preparing a magnetic
recording medium of the present invention by a vapor deposition
method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The above defects can be avoided upon using iron and cobalt as
ferromagnetic metals contained in a magnetic layer and forming a
nitrogenated and oxidized thin film by combining iron and cobalt
partially with nitrogen and oxygen and by properly defining the
composition of the above-described iron, cobalt, nitrogen and
oxygen within a predetermined range.
That is, the present invention relates to a magnetic recording
medium comprising a non-magnetic support over which there is formed
a thin ferromagnetic metal film mainly comprising iron and cobalt.
The thin metal film also contains nitrogen and oxygen, and when the
contents (atomic percentages based on the total number of the
following atoms) of iron, cobalt, nitrogen and oxygen are
represented in terms of a, b, c, d, (that it, FE.sub.a Co.sub.b
N.sub.c O.sub.d) the contents meet the following limits:
In this magnetic recording medium, it is preferred that the
contents (atomic percentages) of iron, cobalt, nitrogen and oxygen
contained in the thin metal film are within the following
restricted ranges:
It is further preferred that c is about 10 and d is from 10 to
17.
The structure of the metal thin film containing iron, cobalt,
nitrogen and oxygen are unclear, but they are believed to be a
mixture or a composite substance of pure iron, pure cobalt, iron
nitride, iron oxide, cobalt nitride and cobalt oxide.
Various structures of iron nitride Fe.sub.x N are known.
Ferromagnetic iron nitride is in the form of Fe.sub.4 N and
Fe.sub.8 N (which is also represented as Fe.sub.16 N.sub.2). When
the contents of the above-described compositions fall within the
ranges as defined above, it is possible to form a magnetic
recording medium having a nitrogenated and oxidized thin film with
high saturation magnetization having good environmental resistance
and anti-corrosive property.
A magnetic vapor deposited film can be formed as a magnetic layer
of a thin metal film on a non-magnetic support by a so-called
inclined vapor deposition method. That method comprises heating an
iron cobalt alloy contained in a crucible with electron beams and
the like, thereby vaporizing iron and cobalt atoms, and jetting the
resulting ion stream flow on the non-magnetic support at an
inclined angle preferably of not less than 20.degree. and more
preferably of 30.degree. or more. In this instance, ion beams
containing at least nitrogen ions formed by an ion gun are
introduced to the vapor deposition area so that ion beams react
with iron and cobalt particles. Oxygen may react as an ion with
nitrogen ions in the stream flow, or may be present as an
atmospheric gas at the vapor deposition area.
Regarding the ratio of elements contained in the magnetic layer,
the ratio of iron and cobalt is controlled by adjusting the power
of the electron beams and by adjusting the composition of alloy.
The ratio of nitrogen and oxygen is controlled by adjusting the
amounts of nitrogen gas and oxygen gas supplied in an ion gun or by
adjusting the residual gas pressure in a vacuum bath.
The sole FIGURE shows an exemplary apparatus for forming a thin
metal film of the present invention. In a vacuum chamber 1, there
are installed a system for conveying a non-magnetic support 2 and
underneath it, a vapor source and an ion source for introducing
metal vapor flow and nitrogen oxygen ions. The non-magnetic support
2 is conveyed along the periphery of a cylindrical drum 4 through
transporting rollers 3. An iron cobalt alloy 7 is put as a vapor
deposited material in a crucible 6. An electron beam from an
electron gun 8 is directed to the iron cobalt alloy 7 to vaporize
the iron and cobalt atoms. The resutling vapor flow jets to the
travelling support 2 at an inclined angle through a mask 5. Gas
containing nitrogen is introduced through a source line 12 into an
ion gun 9 which ionizes the nitrogen and the ion beams are shot to
the vapor deposition area. At the same time, gas containing oxygen
is introduced from gas source line 10 or 11 in an appropriate
proportion so that the oxygen partial pressure at the vapor
deposition area is kept constant. The total pressure at the vapor
deposition area depends upon the vaporized amount of the iron
cobalt alloy and the degassing ability of a vacuum pump, but is
generally from 10.sup.-2 to 10.sup.-4 Pa.
The thickness of the magnetic layer in a magnetic recording medium
of the present invention is generally from 30 to 5000 nm,
preferably from 50 to 500 nm.
The non-magnetic support used in the present invention includes a
plastic support such as polyethylene terephthalate, polyimide,
polyamide, polyvinyl chloride, cellulose triacetate and
polycarbonate.
The thus prepared magnetic recording medium must run smooth and
have sufficient durability in a recording and reproducing
apparatus. Accordingly, when the medium is used as a magnetic tape,
a suitable protective and lubricating layer may be provided on the
magnetic layer and a backing layer may be provided on the surface
of the support opposite to the magnetic layer.
The present invention will be illustrated in more detail by the
following Example but should not be limited thereto.
EXAMPLE 1
A magnetic thin film having a 150 nm thickness and containing iron,
cobalt, nitrogen and oxygen was formed on a polyethylene
terephthalate film having a 12.5 micrometer thickness by the
above-described method using the apparatus as shown in the figure.
The angle of incidence at which vapor flow of iron and cobalt were
jetted on a support was between 70.degree. and 90.degree.. When an
iron cobalt alloy having various compositions was vaporized, ion
beams containing nitrogen ions were jetted to form a thin magnetic
film. Samples (Sample Nos. 1 to 5 and Comparative Sample Nos. 6 to
10) having various amounts of oxygen and nitrogen incorporated into
the magnetic thin film were prepared by varying the irradiation
amounts of ion beams containing nitrogen jetted from an ion gun and
by varying the amounts of oxygen gas introduced from the gas
introducing system 10 or 11.
The compositions of samples thus prepared were analyzed by an Auger
electron spectometer ("PHI 560" manufactured by Perkin Elmer Co.,
Ltd.).
As a lubricating agent, stearic acid in an amount of from 6
mg/m.sup.2 to 12 mg/m.sup.2 was coated on the thus obtained samples
and a backing layer containing carbon black was provided thereon.
Thereafter, those samples were cut to a width of 8 mm. Outputs of
those samples at 6 MHz were measured using an 8 mm VTR ("FUJIX-8M6"
manufactured by Fuji Photo Film Co., Ltd.). An 8 mm tape
manufactured by Fuji Photo Film Co., Ltd. was used as a standard
tape.
The anti-corrosive property of those samples was evaluated by
observing the surface of a magnetic layer after a 5% aqueous
solution of sodium chloride was jetted on the samples as a mist and
the samples were allowed to stand at 60.degree. C. and 90% RH for
48 hours. The degree of corrosion was evaluated on three
levels.
A: No corrosion was observed.
B: Slight corrosion was observed.
C: Corrosion was clearly observed.
The results are shown in the following Table.
TABLE ______________________________________ Corrosion resistance
Composition Outputs at against Sample No. a b c d 6 MHz (dB) NaCl
______________________________________ 1 (Example) 40 37 9 14 +7 A
2 (Example) 40 37 5 18 +6 A 3 (Example) 56 20 8 16 +5 A 4 (Example)
56 20 18 6 +5 A 5 (Example) 61 15 8 16 +5 A 6 (Comparative 74 2 9
15 +2 A Example) 7 (Comparative 74 2 1 23 -3 B Example) 8
(Comparative 12 65 9 14 -5 C Example) 9 (Comparative 12 64 1 23 -7
C Example) 10 (Comparative 48 40 8 4 High output A Example)
Fluctuation Standard 8 mm 0 A tape
______________________________________
The magnetic recording medium of the present invention has higher
outputs at 6 MHz than the medium having a conventional iron nitride
oxide thin film and is therefore, suitable for higher density
recording. Regarding corrosive resistance, the present invention is
better than the medium having the conventional iron nitride oxide
thin film and is a s good as a metal tape. When the additive amount
of cobalt is too low, the effects of the present invention cannot
be obtained. However, if the content is raised too high, the
anti-corrosive property deteriorates. Regarding the content of
nitrogen, when the content is too low, the anti-corrosive property
deteriorates, and when the content is too high, the magnetic
properties greatly deteriorate, thereby decreasing the output
levels. Regarding the oxygen content, when the content is too low,
output fluctuations become high. That means that a magnetic layer
wears out with difficulty when oxygen is present in a certain
amount.
While the invention has been described in detail and with reference
to specific embodiments thereof, it will be apparent to one skilled
in the art that various changes and modifications can be made
therein without departing from the spirit and scope thereof.
* * * * *